Post deleted. Made a mistake to think this is still the type of community one can hope for some support when you are in dire straight. Might have been when I first joined. Not worth the ridicule. My bad.

If this is a good investment for you and not just a new toy, put it on credit card and use your earnings to pay back the loan.  You can get a used in EX+ condition 400mm lens from KEH for about $1,000 or you can get a 300mm L lens for $750.  I wish you luck but I doubt a new lens is what you need to succeed, especially a telephoto lens.  What subjects do you need the lens for?  Birds, motorcycle racing, animals way off in the distance?  Those are not normally high demand or highly profitable subjects.

My apologies for not discussing my financial position here in detail for you to understand. Very glad for you that you have a credit card with so much credit on it.

If you ask people for money, they have a right to know I think. Good luck with the project.

No ! Do not believe them. Better give me $ 10.000 and i will do 2 weeks of fantastic holiday on my dream island near indonesia. I will present you some nice images at my youtube chanel. Pictures of my big belly shining in the sun. 

Post deleted. Made a mistake to think this is still the type of community one can hope for some support when you are in dire straight. Might have been when I first joined. Not worth the ridicule. My bad.

I'm not ridiculing you.  If you have a good business plan I would consider helping you out.  For instance if you showed us that you were a terrific wildlife photographer and the only way you could get high selling images is with this lens or if you said you have great connections to get you into some amazing exclusive locations and that lens was necessary.  Right now it seems as though you are saying give me a better lens and I'll take better photos, that isn't a business plan it's wishful thinking.

http://www.lensrentals.com/rent/canon/lenses/supertelephoto/canon-400mm-f5.6l

Why not rent the lens for 5 days it's only $50, take some photos see how they do.  You can add the photos to your site and tell us what kind of earnings potential the images you take have, that way at least it seems like a more a serious effort.  Hoping that getting a new lens will make you money is not a good business plan, you have good enough equipment already.

Oh my the Land of the Nearly Free.
Here that lens is usually c�50 for three days, (from known companies).

At that sort of price, Tickstock's suggestion is Gold.

And second hand is upwards of �800 / $1250 from a company I don't know,  �950 /  $1486 and up from companies I know of.

I tend to agree with Tickstock on this. I would get rid of my 28-105 before I'd sell my 100-400, but that because of my preferred subject choice. It works for me because I don't have models or a studio, so I'm don't make more with shorter lenses, but for most people, the lower range lenses will be more profitable.

It really depends what you're intending to do with your telephoto. If wildlife, look at the existing competition for popular subjects; and look at the sales records (one sites where that is possible) for less popular locations / species. I wouldn't recommend it to a newbie hoping to make the money back in a reasonable timescale, especially nowadays.
Tickstock is right on this too, I'm afraid, even though I use my tele zoom for a lot more than wildlife.